The objectives of this program project include investigations into regulatory mechanisms operating in tissues during craniofacial development (e.g., first and second branchial arch-derived structures with emphasis on tooth morphogenesis). We propose to understand the cellular, molecular and developmental aspects of epithelial determination and differentiation during odontogenesis. Determination leading to secretory ameloblast differentiation reflects exquisite differential gene regulation. We propose to investigate this developmental problem by identifying and isolating the genes that code for enamel proteins. The complexity of the vertebrate genome precludes a direct isolation of enamel structural genes. We propose to physically isolate the mRNAs coding for enamel proteins and to use the complementary DNA probes generated by transcription of the enamel mRNAs to monitor in situ transcription during embryonic, neonatal and postnatal ameloblast differentiation. The value of the tooth organ lies in its high degree of programming for sequential synthesis of unique extracellular matrix proteins derived from either epithelia or adjacent mesenchymal cells. During determination, differentiation and morphogenesis, a program of changing protein synthetic and secretory patterns characterizes odontogenesis. To pursue these problems we propose to investigate the biosynthesis and secretion of fetal and post-natal enamel proteins, determine the role of extracellular matrix as an influencing factor on epithelial gene expression, to localize differential enamel gene expression using in situ hybridization, to determine the variability of enamel genes during vertebrate evolution, and to investigate enamel messenger RNA structures using oligonucleotide probes. This set of issues will employ biochemical, embryological and immunological methods and recombinant DNA technology. These efforts should provide advances toward understanding craniofacial developmental biology and may clarify selected mechanisms related to congenital craniofacial malformations.